In a zinc shot made solely from zinc, a particle-cloud that is produced by shot-crushing has a lower sensitivity to an explosion and its lower boundary for a concentration for an explosion is higher compared with that of aluminum alloy shot or stainless steel shot.
However, the zinc shot is likely to cause a darkening on work to be treated. Also, it has hardness of 40-50 HV in Vickers hardness, and it is soft, such that the effect of a surface treatment is insufficient. So, it takes longer to complete a blasting treatment if the zinc shot is used (Patent Document 1, Paragraph 0004).
To prevent a darkening and to increase the hardness of zinc shot, a zinc-based alloy that has various alloys added to the zinc of the zinc shot is proposed (References 1-6).
To solve these problems, for example, Patent Documents 1 and 2 propose adding Cu, Patent Document 3 proposes adding Ni, Patent Document 4 proposes adding Mn, Patent Document 5 proposes adding Cu and Mn, and Patent Document 6 proposes adding Mg.